1. Field of the Invention
The present invention relates to an apparatus for manufacturing a semiconductor device. More particularly, the present invention relates to a focus ring for focusing plasma or a reaction gas onto a semiconductor wafer.
This application is a counterpart of, and claims priority to, Korean Patent Application No. 1999-41795, filed Sep. 29, 1999, the contents of which are incorporated herein by reference.
2. Description of the Related Art
Conventionally, semiconductor device manufacturing processes such as etching or chemical vapor deposition (CVD) are carried out using a plasma reactor. If the plasma is not distributed uniformly over the wafer, the semiconductor wafer will not be etched uniformly or the layer deposited thereon will not have a uniform thickness. A non-uniform plasma distribution can be caused by non-uniform gas flow across the semiconductor wafer, a non-uniform cathode temperature and/or variations in the intensity in an electric field induced within the reactor, etc. A vacuum pump disposed at the bottom of the plasma reactor continuously exhausts gas to the exterior thereof so that the level of the vacuum in the processing chamber of the reactor is maintained constant. The semiconductor wafer is held by a pedestal or chuck that is located at a center of the processing chamber. Plasma, which is introduced downwardly into the chamber, has a higher flow rate around the semiconductor wafer. Such a plasma reactor is disclosed in, for example, U.S. Pat. No. 5,685,914, entitled A Focus Ring For Semiconductor Wafer Processing In A Plasma Reactor, issued to Graham W. Hills et al. on Nov. 11, 1997.
The focus ring which is the subject of this patent is provided to facilitate a uniform etching of the wafer.
FIGS. 1 and 2 show such a conventional plasma reactor. Referring now to these figures, a vacuum chamber 102 has a gate valve 106 at a sidewall 104 thereof for enabling a semiconductor wafer 110 to enter/exit the chamber 102. The wafer 110 is held by a wafer chuck 112. The periphery of the wafer 110 rests on the wafer chuck 112, and is shielded by a focus ring 114 that surrounds the periphery.
During an etching process, an inner peripheral sidewall 114a of the focus ring 114 locks in charged processing gases on the wafer 110. This enhances the etching process and ensures that the rate at which the wafer 110 is etched is constant. However, the inner peripheral sidewall 114a chemically reacts with the processing gases to create by-products 118. These by-products 118 constitute particulate contaminants 118 in the chamber 102. As successive ones of the etching processes are carried out, the by-products 118 attached to the inner peripheral sidewall 114a grow or increase in number. The by-products 118 eventually fall upon the wafer 110 and thereby contaminate the wafer 110. Thus, these contaminants 118 lower the yield during the mass production of semiconductor devices.
It is therefore an object of the invention to provide a focus ring of an apparatus for processing a semiconductor wafer, which can prevent particulate contaminants adhering to an inner surface of the focus ring from later falling onto the wafer.
To achieve this object, the present invention provides a focus ring having a stepped inner periphery which is formed by a cylindrical bottom surface having a first diameter, a cylindrical top surface having a second diameter greater than the first diameter, and a collector located between the top surface and the bottom surface for collecting contaminants created at the top surface.
The apparatus for processing a semiconductor wafer includes a process chamber, a circular chuck and the focus ring. The chuck is located in the process chamber and holds the wafer. The focus ring focuses processing media onto a surface of the wafer that is held by the chuck. The cylindrical bottom surface of the focus ring extends around that portion of the chuck which supports the wafer.
The collector may form an upwardly facing concavity.
The collector is located beneath the inner upper surface so as to collect particulate contaminants falling therefrom. Thus, the particulate contaminants do not fall onto the semiconductor wafer, whereby the yield of products produced from the wafer is increased. Further, an RF (radio frequency) on time of the apparatus can be extended as much as two times or more the average RF on time of a conventional apparatus, whereby the productivity of the apparatus is enhanced.